Checking The Piston Pin; Installing The Piston And Cylinder - Yamaha XT250X Service Manual

Piston ring end gap
Top ring
End gap (installed)
0.19–0.31 mm (0.0075–0.0122 in)
Limit
0.60 mm (0.0236 in)
2nd ring
End gap (installed)
0.30–0.45 mm (0.0118–0.0177 in)
Limit
0.60 mm (0.0236 in)
Oil ring
End gap (installed)
0.10–0.35 mm (0.0039–0.0138 in)
EAS24440

CHECKING THE PISTON PIN

1. Check:
Piston pin
G
Blue discoloration/grooves → Replace the
piston pin and then check the lubrication sys-
tem.
2. Measure:
Piston pin outside diameter "a"
G
Out of specification → Replace the piston pin.
Piston pin outside diameter
15.991–16.000 mm
(0.6296–0.6299 in)
Limit
15.971 mm (0.6288 in)
3. Measure:
Piston pin bore diameter "b"
G
Out of specification → Replace the piston.
Piston pin bore inside diameter
16.002–16.013 mm
(0.6300–0.6304 in)
Limit
16.043 mm (0.6316 in)
CYLINDER AND PISTON
4. Calculate:
Piston-pin-to-piston-pin-bore clearance
G
Out of specification → Replace the piston pin
and piston as a set.
Piston-pin-to-piston-pin-bore clearance
=
Piston pin bore diameter "b" -
Piston pin outside diameter "a"
Piston-pin-to-piston-pin-bore
clearance
0.002–0.022 mm (0.0001–0.0009
in)
EAS24450

INSTALLING THE PISTON AND CYLINDER

1. Install:
Top ring "1"
G
2nd ring "2"
G
Lower oil ring rail "3"
G
Upper oil ring rail "4"
G
Oil ring expander "5"
G
NOTE:
Be sure to install the top ring and 2nd ring so that
the manufacturer's marks or numbers face up.
2. Install:
Piston "1"
G
Piston pin "2"
G
Piston pin clips "3"
G
NOTE:
Apply engine oil to the piston pin.
G
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